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The Making of the Military’s Standard Arms, Part II

In a post published here last week, we gave an overview of some of the manufacturing operations at Colt Defense LLC in West Hartford, Conn., the only manufacturer of the M-4 for the Pentagon.

The M-4 carbine, one of the primary rifles used by the United States military, appears destined for a change. After concerns surfaced about rifles overheating in a sustained firefight in 2008 in Afghanistan, the manufacturer and the United States Army are close to agreeing on a modification to the weapon’s barrel that makes the carbine more resistant to the stresses of extended firing.

The pair of videos shown below, taken at Colt Defense’s testing range, capture the thinking.

The first video shows an M-4 being subjected to an intensive sustained-firing test. The rifle used is the standard M-4 with a standard barrel. The weapon is secured on a bench and fed one full 30-round magazine after another without rest beyond the time it takes to replace empty magazines with full magazines.

Video

M-4 Firing Test

Watch the video closely. After several magazines, the barrel smolders. Then it becomes red hot. After 1 minute and 20 seconds the barrel begins to droop between magazines — like a piece of warm licorice. Then comes the catastrophic ending, at 1 minute and 51 seconds and after the 535th round, when the barrel ruptures.

It is worth noting that the test simulates conditions that almost no soldier could face. In it, 18 magazines are fed through the rifle in less than two minutes. Soldiers and Marines armed with an M-4 or M-16 (the carbine’s longer-barreled parent) typically carry seven or so magazines.

Moreover, the M-4 carbine used in the test had been modified to fire fully automatically. As long as the shooter holds back the trigger, the test rifle keeps firing until the magazine is empty. Standard-issue M-4s fire only on semi-automatic or a three-round burst setting, not like this.

For these two reasons, it would be impossible for a soldier armed with a standard M-4 to fire as many rounds in such a short period of time — even with the ammunition, even with the desire. The rifle is undergoing a test similar to running an automobile engine at, say, 50,000 or more r.p.m.s.

Still, when set against the second video, the test has comparative value.

That video shows the same test with an M-4 equipped with a thicker, heavier barrel, which is used on a specialized carbine, known as the M-4A1. This variant is carried by some Special Operations users.

Video

M-4A1 Firing Test

Naturally, the rifle still overheats. Heat is an unavoidable byproduct of the cartridges’ burning propellant. It cannot be avoided. But look at what happens with the M-4 outfitted with a heavier barrel.

The barrel gets hotter and hotter, and the heat spreads throughout the weapon. The shooter wears a heat-resistant glove even to pull the trigger. Soon the barrel smolders and glows, but it does not droop and does not rupture. At 2:22 the hand guard assembly catches fire. It burns for about two and a half minutes. But the rifle keeps firing, magazine after magazine, until it stops firing on automatic at 4 minutes and 47 seconds, after 911 rounds.

The reason for the stoppage is that the gas tube, which is located under the upper hand guard, has ruptured. The tube is essential. It diverts a portion of expanding gases associated with each discharged cartridge back toward the carbine’s bolt. This excess energy, aided by springs, is converted to the many steps required for automatic or semiautomatic fire.

With the gas tube ruptured, the shooter continues to fire the rifle several times manually. But at this point, more than 900 rounds after the shooting began, the rifle is a red-hot single shot weapon -– and no longer an infantry assault rifle that can perform as intended.

Even if the sort of extreme firing seen in these videos exceeds the rate of fire that can be achieved in combat, the takeaway is clear: increasing the thickness of an M-4’s barrel increases the rifle’s ability to function in sustained, intensive combat.

Colt Defense and the Army have been discussing making the change to a heavier barrel for several months and appear likely to begin requiring standard-issue rifles to have the barrel previously manufactured for the M-4A1.

If the change is made, the standard M-4 will retain its semiautomatic and burst modes of fire. It will not fire automatically.

Because both the lighter and heavier barrels are machined from identical sleeves of steel (the thicker barrel, in the simplest sense, spends less time on the lathe), the change can be made without increasing the cost per rifle.

The downside is that the heavier barrel would increase the weight of a standard M-4 by five ounces. The Army has all but decided the trade-off is worth it, and seems to be considering not whether it should require new carbines to be manufactured to this standard, but whether it should retrofit the hundreds of thousands of rifles already in the services’ possession.

“The bottom line is that we are going to do this,” Colonel Douglas Tamilio, who supervises small arms development for the Army, said of the change to new carbines. “We have to get all of the services to buy in, but it adds five ounces in weight and doubles your sustained rate of fire.”

He added, “I think it’s a no-brainer, and we’re going to see it in the near future.”

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